Lime plaster is a traditional building material which, in basic terms, is made by burning limestone, then slaking it with water to form a plaster that hardens with age. It has been used for thousands of years, and when fully cured is extremely durable and hard-wearing. In fact there is evidence of lime being used for ancient Egyptian monuments, and the Romans used it regularly.

 

New lime plaster is highly caustic and usually requires specialist application, but when successfully applied it provides a highly breathable, flexible but very durable substrate. Its high level of breathability makes it ideal for renovation or restoration projects of older buildings where it would have been used traditionally.

 

Unlike modern gypsum plaster, lime plaster not only has to dry but also cure, so any ‘coverings’ for lime plastered surfaces should be carefully considered. If you are applying new lime your supplier or specialist plasterer should be able to advise on curing times, but as a general ‘rule of thumb’ we suggest that for every 5mm thickness of lime it needs a minimum of 4 weeks to cure (sometimes longer). This means that no further coatings, whether that’s lime wash, paint, or any other product, should be applied until it has had sufficient curing time.

 

          

 

Which finish is best for lime?

 

There are various finishes for lime substrates, each with different characteristics; limewash being the most traditional choice. Limewash is used not just to add colour to lime plastered walls but also to protect the substrate underneath. Its microporous, alkaline properties deter algae growth, making it an excellent choice for heritage projects. Many traditional builders and conservation specialists recommend limewash because it is the most authentic finish for lime plaster.

 

The main drawback of limewash however, is the level of maintenance involved. It is applied by building up multiple layers, usually with a brush, which can be a time consuming task. It may also require re-application every couple of years or so, therefore not always the most practical option in the long-term.

 

If you are looking for an alternative to using limewash on interior walls, ensure you opt for a breathable paint for lime plaster. Claypaint has a very high level of breathability that is it fully compatible with lime. It is available in a far greater range of colours than most lime washes, whilst the ultra flat matt finish is in keeping with the authentic look of lime surfaces. Plus the thick, creamy consistency of Claypaint has the added advantage of ‘smoothing’ out any hairline cracks or irregularities in the surface.

 

Image: Rocky Horse

How to paint interior lime plastered walls with Claypaint:

 

• 1. Dampen the plaster immediately prior to painting using a damp cloth, wet brush or roller, or a water spray bottle.
• 2. Apply a mist coat of paint by diluting the Claypaint with 20% water. Mix thoroughly before applying.
• 3. When dry apply 1-2 full coats of Claypaint using a short pile roller for a smooth, consistent finish.

 

What about exterior lime walls?

 

Lime wash remains the traditional choice for finishing exterior lime plastered or lime rendered surfaces. However the level of maintenance outside can be even greater as walls are less protected from the elements. The upkeep of lime wash, which sometimes flakes over time, can be a real problem if your property is regularly exposed to windy or wet conditions.

 

 

Our Ecopro Silicate Masonry System is a breathable, viable alternative for external lime substrates. It is a simple two part system consisting of primer and paint, which once applied is incredibly long lasting. Unlike lime wash, Ecopro Silicate Paint will not peel or flake yet still remains moisture-permeable, enabling water vapour to pass easily through the substrate thus allowing your property to breathe.

 

Many of our stockists are experts in traditional building and decorating techniques, a number of whom specialise in lime products, providing raw materials and advice. We would always suggest seeking advice from a professional who has experience with lime. If you have any questions give us a call, drop us a line or chat to any of our lovely stockists.